At the LHCb experiment [1]}, the inclusive \(\tau ^-\)  production cross-sectionThe inclusion of charge conjugate processes is implied throughout. is large, such that in one nominal year of data taking
a factor of \(\sim 100\)  more \(\tau ^-\)  leptons are produced than in the total samples collected over the lifetimes of the BaBar and Belle experiments.
This, combined with the clean detector signatures provided by final-state muons, makes searches for decays such as \(\tau ^-\rightarrow \mu ^+\mu ^-\mu ^-\)  particularly
promising. The current world's best limit on the branching fraction for \(\tau ^-\rightarrow \mu ^+\mu ^-\mu ^-\)  is \(2.1\times 10^{-8}\)  at 90% confidence level (CL) from Belle [2]}.
